Here, the term “gear pump” designates a system composed of two intermeshing toothed wheels for the propulsion of a liquid. A simple gear pump is illustrated in FIG. 1. The simple gear pump comprises two toothed wheels, which are arranged side by side in a cavity or a pump body, which is eight-shaped. The toothed wheels mesh by rotating in opposite directions relative to each other. The body comprises an inlet and an outlet for the passage of the fluid to the right of the meshing zone of the toothed wheels. The fluid is housed between the teeth of each of the wheels and the wall of the body of the pump. The fluid cannot return between the two wheels, which drive this fluid at the periphery of the cavity. The gear pump uses the combined profile of two toothed wheels to transfer and increase the pressure of the fluid.
The document U.S. Pat. No. 6,991,442 filed by Soqi Kabushiki Kaisha describes a gear pump, a section of which is illustrated in FIG. 2. The two toothed wheels 37, 38 having parallel axes of rotation 39, 41 of the gear pump are housed in a pump body or a cavity 36, which is connected to a hydraulic system comprising an oil pan 68, an oil supply means 35, pipes 62, 63, 66, 67, grooves 64 and 65, and valves 69. The chassis of the gear pump comprises three flat metal plates 48, 49, 51. These plates are placed one above the other, with the intermediate plate 49 in the middle, which includes the cavity 36 in order to house the gear pump. Screws 52, 33 releasably connect these three plates 48, 49 and 51. Furthermore, pins 53 serve as a centering in alignment holes in the three metal plates 48, 49, 51 to allow a proper alignment of the three metal plates 48, 49, 51.
The centering pins 53 are located in the peripheral zone of the part, in a dry zone outside the hydraulic circuit.
The intermediate plate 49 is machined in order to form the cavity 36 intended for the gear pump. The two other peripheral plates 48 and 51 are placed below and above the intermediate plate 49 housing the pump. The fact that the plates 48, 49 and 59 are made of metal allows obtaining a good accuracy, which ensures desired performances in terms of pressure of the fluid downstream of the pump.
Grooves and pipes for the hydraulic system are also machined in these three plates before assemblies. Thereby, one of the drawback of this pump is that the path of the fluid passes through substantially right angles, at 90°, see the marks 62 and 63, which leads to internal pressure drops. It would be possible to remedy partially this problem by machining radii or fillets, but at additional costs.
Another drawback of the hydraulic pump described in U.S. Pat. No. 6,991,442 is the eccentric location of the centering pins, which increases the bulk of the gear pump.
Moreover, a manufacturing of the hydraulic chamber made of plastic, in particular of injected thermoplastic, which is another known embodiment, does not allow obtaining the same accuracy as a metal part and leads to insufficient or irregular performances because of the dispersion of the clearances obtained during manufacture.
There are also in the state of the art pumps with components made of thermoplastic rectified with high dimensional accuracy, but these operations are very expensive.